[PublicAPI] public static IRxVal <Option <B> > mapT <A, B>( this IRxVal <Option <A> > rxMaybeA, Fn <A, B> f ) => rxMaybeA.map(maybeA => maybeA.map(f));
public static IRxVal <A> filter <A>(this IRxVal <A> rx, Fn <A, bool> predicate, A onFiltered) => rx.map(RxVal.filterMapper(predicate, onFiltered));
public static IRxVal <Option <B> > optMap <A, B>( this IRxVal <Option <A> > source, Fn <A, B> mapper ) => source.map(aOpt => aOpt.map(mapper));